TxDOT to take roundabout approach to congestion at East 51st and I-35

Updated Nov 26, 2015

For drivers facing stacked-up traffic on southbound Interstate 35, the ramp to East 51st Street can seem like a tantalizing exit strategy, a way to get around a mile or so of congested highway.

Then, up ahead and around a right-hand swerve in the frontage road, they encounter the East 51st intersection, and the real wait begins.

“As anyone who drives through that intersection today knows, it is failing,” said Karen Lorenzini, the Mobility 35 program manager for the Texas Department of Transportation’s Austin district. “It does not do a good job of letting southbound traffic through, and a lot of people can end up sitting at that signal for three, four rounds. And a lot of them are only trying to get back on I-35 at the next opportunity.”

So TxDOT, with substantial financial assistance from the city of Austin, plans to install what would be the first “modern roundabout” on any interstate frontage road in Texas. The department, as part of the same project, would also build a frontage road bypass lane under the East 51st overpass, an outlet for some of those people trying to leapfrog congestion that would also mean fewer people up the hill at the new roundabout.

That circle will also ease the westbound-to-southbound path for the ever-growing number of Mueller residents, Lorenzini said. Looking ahead 20 years, she said, TxDOT would have had to install three left turn lanes to handle that load, requiring a wider East 51st bridge.

The $21.6 million project would be the latest example of a marked swing by TxDOT in the past few years toward what it calls innovative intersections — what can be initially confusing variations on the traditional four-way traffic signals drivers now encounter on Texas roads.

Texas 71 at FM 973 in Del Valle led the way with “Michigan left turns,” where the traditional left turn is replaced by a right turn/U-turn combination. Then came “continuous flow” intersections on U.S. 290 in Oak Hill and at two I-35 interchanges in San Marcos, where cars turning left cross oncoming lanes before the intersection and use a new lane on the left side of the road, allowing them to turn without holding up oncoming traffic at the intersection.

Last week, TxDOT opened its first “diverging diamond” intersection in Central Texas, where RM 1431 crosses over I-35 in Round Rock. This design is a complete crisscross: Drivers are routed to the left side of the overpass, which allows them to turn left onto the I-35 onramps without crossing traffic. Through traffic returns to the right side of the road after the overpass.

Now, after the Austin City Council earlier this month agreed to kick in $9.2 million left over from 2010 and 2012 bond elections, TxDOT is getting into the roundabout business.

And a couple of years down the road, the agency hopes to build what it has dubbed the “dogbone” at I-35 and Wells Branch Parkway, essentially three roundabouts in succession between the west side of the highway and the busy fork in the road east of I-35 where FM 1825 splits off from Wells Branch. That project could be open by late 2019, according to a TxDOT master schedule for I-35 renovations.

The roundabout west of I-35 at East 51st, when it is complete in early 2018, will have two lanes around most of its circumference, with three lanes in short intervals. TxDOT officials say it will move 30 to 50 percent more cars at peak periods and eliminate waits entirely during times of light traffic. And, they said, it will be safer.

“It’s constant movement, except when someone has to yield to a pedestrian” at one of several slightly raised crosswalks to be installed in the approaches to the roundabout, Lorenzini said.

But what about the confusion factor? Moviegoers of a certain age might remember the scene from “National Lampoon’s European Vacation” in which Chevy Chase, as hapless dad Clark Griswold, and his family are trapped for hours in a London roundabout.

Lorenzini said TxDOT’s design will be “very intuitive,” leading people seamlessly toward the roundabout exit they want. But to take advantage of that, drivers will have to get in the correct lane as they approach the circle.

“The key is good signage,” she said. That, and experience.

Modern roundabouts, as distinct from the much smaller traffic circles found at a few places in Austin (such as Riverside Drive near the Long Center and in Mueller near the Thinkery), have long been a common design on Western European and Australian highways, Lorenzini said, and are now becoming popular in states such as Indiana, Colorado and Michigan.

As for the safety advantage, TxDOT spokeswoman Kelli Reyna said the key is reducing the number of “conflict points,” essentially spots where vehicles can come together at full speed. Compared with a traditional light intersection, a modern roundabout has only a fourth of the conflict points, she said. And while collisions will still occur in a roundabout, Reyna said, particularly as people get used to that type of configuration, the wrecks tend to be sideswipes and rear-enders rather than the more dangerous T-bone and head-on collisions.

Reyna said that though these designs are still rare in Texas, it would be wrong to think of TxDOT as some sort of tinkerer using the state’s drivers as test subjects.

“It’s not an experimental mode,” Reyna said. “This is the way intersections are going.”